Question

I’m using leaks tool of instruments. It says that I have some leaks in the init method. It shows that NSMutableArray has leak.

I don’t see any leaks.

@interface BookSettings : NSObject
  @property (nonatomic, retain) NSString *title;
  @property (nonatomic, retain) NSMutableArray *authors;
@end

- (id)init 
{
   self = [super init];

   if(self) 
   {
    title           = [[NSString stringWithString:@""] retain];
    authors         = [[NSMutableArray alloc] init];
   }
   return self;
}

- (void)dealloc 
{
 [title release];
 [authors release];
 [super dealloc];
}

Answer 1

The provided code is OK, the problem is somewhere else where authors is retained without a balancing release. Leaks just points to the place ivar is created, not where the missing release should be. Check all the places where the retain count is increased.

If you need to see where retains, releases and autoreleases occur for an object use instruments:

Run in instruments, in Allocations set “Record reference counts” on on (you have to stop recording to set the option). Cause the problem code to run, stop recording, search for there ivar of interest, drill down and you will be able to see where all retains, releases and autoreleases occurred.

Seriously consider using ARC, there is little reason not to, ARC supports back to iOS 4.x.

BTW:

title = [[NSString stringWithString:@""] retain];

can be more compactly written:

title= @"";